1. Field of the Invention
The present invention relates generally to intraocular lenses and more specifically to intraocular lenses having an extended depth of focus.
2. Description of the Related Art
Intraocular lenses are commonly used to replace the natural lens of the eye when it become cataractous. Alternatively, the natural lens may be replaced to correct other visual conditions, for example, to provide accommodation or pseudo-accommodation when a subject develops presbyopia and is not longer able to focus on both distant objects and near objects. In any event, accommodating and/or multifocal intraocular lenses may be used to restore at least some degree of accommodative and/or pseudo-accommodative ability.
Accommodating intraocular lenses are configured to focus on objects over a range of distances by moving axially and/or by changing shape in response to an ocular force produced by the ciliary muscle, zonules, and/or capsular bag of the eye. One problem encountered with accommodating intraocular lenses is an inability to utilize the available ocular forces to produce the full accommodative range typical of a younger eye.
Multifocal intraocular lenses provide a pseudo-accommodation by simultaneously providing two or more foci, for example, one to provide distant vision and the other to provide near vision. Over time, patients with multifocal intraocular lenses generally learn to select the focus that provides the sharper image and to ignore any other blurred images. One problem with multifocal intraocular lenses is a relatively high degree of dysphotopsia (e.g., halos or glare) and reduced contrast sensitivity due to the continual presence of defocused light.
Another approach for providing some degree of simulated accommodation is to extend the depth of focus of a traditional monofocal lens so that objects over a broader range of distances are simultaneously resolve. Again, issues such as contrast sensitivity and reduced contrast sensitivity are typical. Examples of this approach are discuss in U.S. Pat. No. 6,126,286 (Portney), U.S. Pat. No. 6,923,539 (Simpson et al.), and U.S. Pat. No. 7,061,693 (Zalevsky).
Accommodating and multifocal intraocular lenses are needed with enhanced performance and increased design flexibility in addressing the variety of complex issues involved in providing vision to subjects over a wide range of object distances.